We all know what daddy long legs are,
right? Well it might actually be more complicated then you thought. It turns out that some of those spidery
looking bugs might not be spiders at all. There are several species of small
long legged spiders that we have nicknamed daddy long legged spiders, and then
there are creatures that look almost identical, unless you take a closer look
and see that their body looks like a single ball shaped body mass. They go by a
few different names, including Daddy Long Legs, and Harvestmen. They are
actually Opiliones. They are in the class arachnida (8-legged arthropods), but
are in the order Opilione, instead of Araneae which spiders belong to. They are
actually more closely related to scorpions than spiders. The Suborder Eupnoi are those that are most
commonly called daddy long legs and look especially like the long legged
spiders. This is especially true of the superfamily Phalangioideahey
which are commonly seen in the United States and are pictured below. Opiliones
lack an obvious segmentation between their cephalothorax (a fused head and
thorax) and abdomen as spiders do. This is what gives them the appearance of
single ball instead of the two distinctive parts which spiders do. They also
have no fangs, or venom glands, and they do not produce silk as spiders do.
This means that they cannot bite you, inject you with venom, and they do not
build webs. They actually have a pair of sent glands near their eyes that
secrete a stinky liquid that gets into a predator’s eyes and mouth. What they
can do is pinch you with their chelicerae (similar to crab pincers) and some
can even squeeze their back legs together hard enough to give a nasty pinch. Some
are also covered with sharp spines that can induce bleeding. They experience
their world mostly through touch, which they use their legs to do. Some Opiliones
have short legs, but many of them have very long legs which they use to explore
their surroundings, anticipating a potential meal, or avoiding a threat. If one
of these legs gets unfortunately caught by a predator, as a last resort they
can lose that leg and flee. These do not grow back but they can lose multiple
and still live a relatively successful life. 
Spiders have several eyes, situated in
many different ways, but Opiliones only have two and they sit on a raised
service on the top of their head. In some species there is also a ridge of
bumps or spikes over each eye that can look markedly like an eye brow. There
around 7,000 different species of Opiliones around the world, many of them
being endangered.
Next time you see those long legs
ambling about, take some time and look a little closer. Are you looking at a
spider like you had always thought? Or something entirely different, an
Opilione.
Sources
-Kury, A.B. (2000 onwards) Classification
of Opiliones. Museu Nacional/UFRJ website. Online at:
http://www.museunacional.ufrj.br/mndi/Aracnologia/opiliones.html
Images Sources
-Kury, A.B. (2000 onwards) Classification
of Opiliones. Museu Nacional/UFRJ website. Online at:
http://www.museunacional.ufrj.br/mndi/Aracnologia/opiliones.html
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